The goal of exploration
seismologists is to obtain the reflectivity model of the earth.
This is partly achieved by collecting non-zero offset seismic data
in the format of CSG's, reorganizing them into
CMG's, filtering these data, applying static and NMO time
shifts to correct these data to the ZO time, and stacking
to get the poststack seismic section. The stacking process is the most
powerful step in eliminating both coherent and random noise. For this reason and
to also increase spatial resolution,
offset traces with
source-receiver offsets out to more than
several miles are not uncommon and sections with more than
100 fold are also used.
To get an even better approximation to m(x,z) the migration
operator LTd is applied to these data.

Assumptions implicit in the data processing include:

Data are largely governed by the acoustic isotropic wave equation, where
density variations are weak.

Primary reflections only in the stacked section. This means
that the processing has largely eliminated
coherent noise such as multiples, converted PS reflections, surface waves, etc..

Velocity distribution is known in order to properly
migrate data. Velocity semblance analysis
usually does a pretty good job for geology that is not too
complex.

No reflection events originate from out-of-the-recording plane are
in the data. Otherwise 3-D data should be collected and processed in a 3-D fashion.